1. Field of the Invention
The present invention relates to spring motors, and in particular to spring motors commonly referred to in the industry as "B" motors, i.e., motors which have a substantially constant output torque.
2. Description of Related Art
Spring motors have been used in many applications such as in clocks, retractable tapes, wind-up toys, turntables for microwave ovens, etc.
A known spring motor includes an output drum rotatably mounted on an axle. Adjacent to the output drum is a storage drum, similarly rotatably mounted on an axle substantially parallel to the output drum axle. A tightly coiled noncumulative force ribbon spring is normally coiled on the storage drum. The inner end of the ribbon spring is connected to the storage drum by inserting the end into a slot in the storage drum.
The other end of the ribbon spring is riveted to the output drum in such a way that the ribbon spring can be wound onto the output drum in a reverse direction relative to the winding on the storage drum.
A spring motor of the above description is disclosed in U.S. Pat. No. 3,151,704, issued on Oct. 6, 1964 to Clarke. Similar spring motors are disclosed in U.S. Pat. No. 2,063,799, issued on Dec. 8, 1936 to Fornelius et al and in U.S. Pat. No. 2,673,694 issued on Mar. 30, 1954 to Howell.
In the known spring motors, the spacing between the mounted drums is not adjustable because the positions of the two axles are fixed. Therefore, those motors may require a relatively large amount of space.
U.S. Pat. No. 2,869,801, issued on Jan. 20, 1959 to Foster, discloses a spring motor having a pair of springs, each with a respective output drum. One end of each spring is mounted on its respective output drum in a conventional manner. The other end of the spring is simply tightly coiled so as to rest adjacent the output drum. A pin is provided adjacent each output drum to limit movement of the coils. A particular problem with this spring motor is that if it is wound too much, the free end of each spring will pass between its adjacent pin and output drum which would cause jamming of the motor.